The invention relates to vehicle suspension systems for dual axle vehicles in which the axles are attached to equaliser beams or more commonly known as walking beams, so that the vehicle load is transferred to the road surface either equally, or in proportion, to the position of the beam pivot to the beam centre.
Various vehicle suspensions have been developed for dual axle vehicles in which the axles are attached to walking beams with a springing medium located between the beam pivot and the vehicle chassis to absorb shocks caused by uneven road conditions. Additionally a mechanical connection system is used between the walking beam and the chassis to firstly transmit tractive effort and torque; secondly to absorb braking effort and torque; and thirdly to constrain the lateral relationship of the axles with the chassis. In the case where the springing mechanism uses steel springs, the spring is usually a multi-leaf semi elliptical type or a taper leaf type, having an eye at the forward end and a slipper surface at the rear end. The spring and its associated saddle then performs all or part all of the required functions of the mechanical connection system. In the case where the springing mechanism uses rubber springs, or air springs, the mechanical connection systems are usually vertical drive pins and load cushions located in vertical aligned rubber bushings.
Air suspensions are generally recognised as having desirable features including superior ride comfort for the driver; enhanced impact protection for the vehicle and cargo; and reduced road impact and consequent road wear. Air suspension with walking beams and vertical drive pins have the benefits of previously mentioned desirable features reduced because the vertical drive pins and associated bushings tend to restrict vertical freedom of the suspension.
It is an object of the invention to provide a suspension system which combines the advantages of both a walking beam suspension which incorporates air spring(s).
A further object of the invention is to provide a suspension system which provides a simple way of converting an existing walking beam suspension from mechanical springing to air springing.
With these objects in view the present invention in a first aspect provides a suspension system for installation between a chassis and dual axles of a vehicle, said suspension system including an equaliser beam pivotally linking said axles together, a trailing arm support member pivotally attached to a hanger bracket on said chassis, a suspension saddle secured to said trailing arm support to provide pivotal support for said equaliser beam and air spring means located between said chassis and said trailing arm support member.
Preferably said trailing arm support member is formed from a steel fabrication, a nodular iron casting or a spring steel. In a preferred embodiment said suspension saddle is located below said trailing support member and said air spring means is located on the opposing side of said trailing support member. In a practical embodiment the pivotal attachment of said trailing arm support member to said hanger bracket includes a releasable offset cam member to provide axle alignment adjustment.
In a further aspect of the invention there is provided an axle adjustment system for vehicle suspension, said axle adjustment system including a hanger bracket for attachment to the chassis of said vehicle, a suspension element pivotally attached to said hanger bracket, a pivot pin releasably located within said hanger bracket and having a cam element for engagement with said suspension element whereby rotation of said pivot pin causes relative movement between said suspension element and said hanger bracket.